1. Field of the Invention
This invention relates to a process of calibrating a noninvasive blood glucose sensing monitor. In this invention, a process for calibrating a blood glucose monitor for an individual patient is described. This process provides a means for achieving the exquisite control or management of both signal as well as noise within the noninvasive measurement during calibration and subsequently during the long-term use of the calibrated device by humans desiring to monitor their level of blood glucose on demand.
2. Background Art
U.S. Pat. Nos. 5,070,874; 5,360,004; 5,379,764; 5,471,981; and 5,460,177 describe methods for the noninvasive measurement of blood glucose levels. In general, these methods use a spectrophotometer to measure the absorbance of near-infrared radiation at different wavelengths across the range of interest. The absorbance plotted against the wavelengths constitutes a spectrum. By analyzing the spectrum, the blood glucose levels, or changes thereto, can be determined. As the blood glucose levels vary, the detected spectrum also changes.
It is generally known that calibration of analytical devices can be accomplished through using univariate or multivariate mathematical/statistical analysis methodology. As such, reports of noninvasive blood glucose sensing have demonstrated the correlation of measurements of spectroscopic measurements obtained noninvasively with an alternative method known as a reference method requiring invasive and often painful sample collection. While much previous work deals with the process of calibration leading to interesting mathematical/statistical correlations, mathematical models have not yet been shown to be useful for reliable prospective glucose tests of a diabetic patient's blood glucose.
Previous reports on noninvasive glucose sensing have not proven that prospective noninvasive glucose determinations using these methods possess sufficient accuracy to allow the newly emerging technology to serve as a replacement of older invasive technology. By "prospective" testing, we mean that the glucose test results are followed forward in-time, allowing evaluation of long-term accuracy. Prospective testing involves evaluation and continuous monitoring of independent glucose tests as additional time lapses after first establishing the calibration. Previous reports have not demonstrated that the noninvasive technology can maintain model stability to the extent that these independent test results can remain accurate even as time elapses after the initial creation of the calibration model.
In previous calibration methods, data from numerous patients has been collected to calibrate a glucose monitor to a theoretical "norm". Test results from an individual patient were then compared to this norm to try to calculate that individual patient's glucose level. However, calibration using data obtained from a multitude of patients to prospectively measure glucose in any one patient has not been successful. This is mainly due to the large person-to-person variation in the morphology, physiology and chemistry of the skin.
Therefore, it is an object of the invention to provide a method of individually calibrating a noninvasive blood glucose sensing device to overcome the problems associated with patient-to-patient variability and also variability with an individual patient. It is also an object of the invention to provide a personalized calibration method that spans a patient's skin, spans time between readings and spans glucose variation inherent in a diabetic condition.